emulators/unicorn: fix build on powerpc64 elfv2 and powerpc64le

As with other ports, conflicting symbols first need to be undefined before including altivec.h.

emulators/unicorn/files/patch-qemu_include_qemu-common.h

@@ -0,0 +1,18 @@
+--- qemu/include/qemu-common.h.orig	2020-10-24 17:16:21 UTC
++++ qemu/include/qemu-common.h
+@@ -205,7 +205,6 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b
+ 
+ /* vector definitions */
+ #ifdef __ALTIVEC__
+-#include <altivec.h>
+ /* The altivec.h header says we're allowed to undef these for
+  * C++ compatibility.  Here we don't care about C++, but we
+  * undef them anyway to avoid namespace pollution.
+@@ -213,6 +212,7 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b
+ #undef vector
+ #undef pixel
+ #undef bool
++#include <altivec.h>
+ #define VECTYPE        __vector unsigned char
+ #define SPLAT(p)       vec_splat(vec_ld(0, p), 0)
+ #define ALL_EQ(v1, v2) vec_all_eq(v1, v2)